1. Field of the Invention
This invention particularly relates to improvement of flow of hydrocarbons such as crude oil or refined products in constricted conduits such as pipelines. It is presently believed to be of particular importance in the oil industry.
More particularly, it is directed to a method and composition for introduction into flowing streams of hydrocarbons such as crude oil or petroleum in a pipeline or refined products in a pipeline whereby the flow improver is readily dissolved into the flowing hydrocarbons, thus avoiding problems of the prior art relating to the necessity of transportation of hazardous materials and the notorious difficulty of dissolving effective flow improvers or drag reducers into flowing hydrocarbons. The stable nonagglomerating suspensions of the invention and the process for employing such suspensions go far toward resolving field difficulties.
This invention relates to copending application number U.S. Pat. No. 5,449,732 issued Sep. 12, 1995, relating to the preparation and use of non-crystalline, high-molecular weight, hydrocarbon soluble, polymers useful for drag reduction or flow improvement of flowing hydrocarbon streams, entitled "Solvent Free Oil Soluble Drag Reducing Polymer Suspension". In particular, that application discloses in detail one presently preferred method for preparing the finely divided polyalkenes of this invention.
This invention also relates to U.S. Pat. No. 5,376,697 issued Dec. 27, 1994, relating to the preparation and use of non-crystalline, high molecular weight, hydrocarbon soluble, polymers useful for drag reduction or flow improvement of flowing hydrocarbon streams, entitled "Drag Reducers For Flowing Hydrocarbons", and herewith incorporated by reference herein. In particular, that application discloses in detail another presently preferred method for preparing the finely divided polyalkenes of this invention.
By way of background, it is known that certain polymers which are oil soluble may be polymerized in the presence of catalysts to produce high molecular weight non-crystalline hydrocarbon soluble polymers by various means. These polymers, when dissolved in a hydrocarbon fluid flowing through a conduit, greatly reduce turbulent flow and decrease "drag" thus reducing the amount of horsepower needed to move a given volume of hydrocarbons, or conversely enable greater volumes of fluid to be moved with a given amount of power. In short, these polymers are drag reducers or flow improvers. Further, dilute solutions of high molecular weight polymers and solvents such as hydrocarbons, display useful flow characteristics unusual to the commonly known crystalline, largely non soluble, artifact-forming polymers such as polyethylene and polypropylene. In particular, these hydrocarbon soluble materials are noted for their effectiveness as drag reducing agents and anti-misting agents. An anti-misting agent is a polymer which, when dissolved in a hydrocarbon, serves to significantly increase medium droplet size and thereby reduce flammability of fuel sprays caused by high velocity wind shear, such as that which occurs during rupture of a fuel cell resulting from an impact such as an airplane crash.
One important characteristic of such polymers is their susceptibility to shear degradation when dissolved in hydrocarbons. Thus, passage through a pump, severe constrictions in a pipeline or the like where turbulent flow is encountered can shear the polymer and thereafter reduce effectiveness, in some cases dramatically so. Consequently, it is important that these polymers be placed into the flowing hydrocarbon stream in a form which achieves certain desirable features.
The polymer should be placed in a form adequate for easy transportation and handling without exotic or unusual equipment, since injection points for the polymer into the flowing hydrocarbon stream can often be at remote and inaccessible locations. The polymer must also be in a form which dissolves rapidly in the hydrocarbon being transported, since the polymers have little drag reducing effect until solubilized into the hydrocarbon stream. The polymer should also be innocuous to the ultimate purpose of the hydrocarbon fluid. For example, in the case of a crude oil flowing through a pipeline, larger amounts of water and contaminants can be tolerated than in finished pipeline products such as diesel fuel or gasoline which are ultimately destined to be burned in internal combustion engines and the like.
At the present time, a number of different commercial approaches have been taken to the problem of preparing, dissolving, transporting and using such drag reducing polymers. In use, these polymers form extremely dilute solutions (ranging from about 1 up to about 100 parts per million polymer in hydrocarbon) which are effective in order to achieve drag reduction or anti-misting. The common commercial method is the preparation of dilute solutions of polymer in an inert solvent such as kerosene or other solvating material as set forth in Mack, U.S. Pat. No. 4,433,123. Mack utilized a solution of high molecular weight polymer suitable for use as a drag reducing agent when produced by polymerization of alpha olefin in a hydrocarbon solvent. The entire mixture, containing polyolefin, solvent, and catalyst particles, is used without separation to form dilute solutions of the polymer in crude oil or other hydrocarbons. However, one disadvantage of such an approach is the use of a solvent, which poses a shipping and handling difficulty and may constitute a hazard. In addition, the product itself forms a gel-like substance which is difficult to introduce into flowing hydrocarbon streams and which becomes extremely viscous and difficult to handle under cold weather temperature conditions at some pipeline injection points.
In addition, it has been found necessary to terminate solution polymerization process reactions at no more than 20 percent polymer based on total reactor content by weight in order to obtain the high molecular weight polymers which are most effective, as taught in U.S. Pat. Nos. 4,415,714, 4,493,903, and U.S. Pat. No. 4,945,142.
A second approach is to prepare the polymers as a solid material as described in the Weitzen patent, U.S. Pat. No. 4,340,076. Weitzen taught that a high molecular weight polymer would be very rapidly dissolved in solvents if the polymer was ground in the solvent while below the glass transition point of the polymer. Polymer concentrations as high as 15 percent or more could be obtained, and only a few parts per million were needed in the flowing hydrocarbon stream for drag reduction or flow improvement. Three patents issued to O'Mara et al, U.S. Pat. Nos. 4,720,397, 4,826,728, and U.S. Pat. No. 4,837,249 all deal with finely grinding or reducing the polymers to very small particle size in an inert atmosphere below the glass transition point of the polymers in the presence of a partitioning agent to form a multi-layered coating which holds the inert atmosphere adjacent to the polymer particles after being ground. The patent teaches that it is mandatory that the reduction to fine particle size be carried out in an inert atmosphere utilizing a refrigerant such as liquid nitrogen and a coating agent while grinding the polymer to a size of less than 0.5 millimeters or about 35 mesh. This process requires that particles be maintained in an inert atmosphere without contacting water or oxygen until dissolved in the hydrocarbon solvent.
Thus, it is necessary either to have an impervious particle coating which prevents air or water from contacting the particle until dissolved, or the entire system must be maintained under an inert atmosphere until the material is dissolved. It can be seen to be bulky and cumbersome, especially at remote pipeline locations.
In a most successful commercial approach, the entire reaction mixture of a polymerization process, comprising a high molecular weight polymer dissolved in a polymerization solvent such as hexane, heptane, or kerosene in a concentration ranging from as low as 2 to 3 percent to a maximum of about 12 percent is utilized. While this material has proven to be difficult to pump under cold weather conditions, it is presently the most economical way to utilize polymer reaction products as drag reducing materials for flowing hydrocarbons.
All commercial processes or known processes to date for the preparation of polymers useful for drag reducing or flow improving purposes have a significant disadvantage. The ultra-high molecular weight materials which impart the best drag reduction or flow improvement in the flowing hydrocarbon streams are notoriously hard to dissolve. Either method requires additional equipment not normally utilized in pipeline locations and pump stations, and requires significant handling equipment investment. For example, U.S. Pat. No. 3,340,076 requires a source of liquid nitrogen for its operation. This substantially adds to the cost and difficulty of employment. The limitation on polymer content of 10 to 15 percent in current commercial processes also means that a great deal of shipping cost is incurred relative to the active polymer content.
2. Description of the Prior Art
Drag reducing polymers are described in the art. Representative but non-exhaustive examples of such prior art are U.S. Pat. No. 3,692,676, which teaches a method for reducing friction loss or drag for pumpable fluids through pipelines by adding a minor amount of the high molecular weight non-crystalline polymer. U.S. Pat. No. 3,884,252 teaches the use of polymer chunks as a drag reducing material. These materials are extremely visco-elastic and are not suitable for forming injection molded or blow molded articles. In general, these polymers have no known use other than drag reducing materials and anti-misting agents. The very properties that make these materials extremely effective as drag reducing additives make them extremely difficult to handle since they have a severe tendency to cold flow or reagglomerate, generally into a sticky mass.
The general propensity of non-crosslinked polymeric material to cold flow and reagglomerate is well known. Numerous attempts have been made to overcome the disadvantages inherent in solid cold flow in polymers. Representative but non-exhaustive of such art is that described in U.S. Pat. No. 3,791,913 when elastomeric pellets were surface cured to a minor depth in order to maintain the unvulcanized interior of the polymer within an enclosure of cured material in each pellet. U.S. Pat. No. 4,147,677 discloses a method of preparing a free-flowing finely divided powder of neutralized sulfonated elastomer by mixing with fillers and oils. U.S. Pat. No. 3,736,288 teaches solutions of drag reducing polymers in inert normally liquid vehicles for addition to liquids flowing in conduits for achieving a staggered dissolution effect by varying the size of the polymer particles. Suspending with surface active agents is also known. U.S. Pat. No. 4,340,076 discloses a process for dissolving high molecular weight hydrocarbon polymer in liquid hydrocarbons by comminuting the polymer into discreet particles and contacting these materials at near cryogenic temperatures with the liquid hydrocarbons to more rapidly dissolve the polymer. U.S. Pat. No. 4,584,244 cryogrinds drag reducing polymers under liquid nitrogen with alumina to obtain a free-flowing friable solid drag reducing composition.
U.S. Pat. Nos. 4,720,397, 4,826,728, and U.S. Pat. No. 4,837,249 deal with processes and compositions relating to a rapidly dissolving polymer composition or to polymer cryoground below glass transition temperatures and freshly cleaved surfaces in an inert atmosphere with a coating which holds the inert atmosphere adjacent to the polymer until dissolved in hydrocarbon.
Of the disclosures known to the inventors, perhaps U.S. Pat. No. 4,212,312 is the most nearly related to the invention at hand. It discloses forming drag reducing polymers which are particulated by dissolving the polymers into a low boiling solvent which is water immiscible together with surfactants to form an emulsion and thereafter removing the solvent from the emulsion by flashing.
U.S. Pat. No. 3,736,288 also has some relevance to the invention at hand. The patent discloses slurry formation of a water-soluble polymer drag reducer. The formulation comprises:
(a) a particulate water-soluble ethylene oxide polymer, PA1 (b) a water-miscible, non-solvent, organic vehicle, PA1 (c) a suspending agent, and PA1 (d) a surfactant. PA1 (a) water, PA1 (b) highly dispersed in the water, and substantially insoluble therein, an extremely finely divided, non-crystalline, ultra-high molecular weight, hydrocarbon-soluble, undegraded, polyalkene having 2 to about 30 carbon atoms per alkene precursor and an inherent viscosity of at least about 20 dL/g, and PA1 (c) a small but effective amount of surfactant having a HLB balance of at least about 9 is introduced into a hydrocarbon stream. PA1 (a) combining at least one alkene containing from 2 to about 30 carbon atoms with a polymerization catalyst in the substantially complete absence of oxygen and water in an impermeable organic polymer reaction enclosure capable of substantially preventing passage of oxygen and water, the enclosure being of such size and shape as to effect high heat conductivity from the reaction enclosure contents to the exterior environment, PA1 (b) polymerizing the alkene while removing sufficient heat from the reacting polyalkene in the reaction enclosure to maintain the reaction at a temperature suitable for production of non-crystalline, high molecular weight polyalkene for a time sufficient to obtain such polyalkene at a level of at least 90 percent by weight based on total reaction content weight, PA1 (c) cooling the obtained polyalkene and the enclosure to a cryogenic temperature, and PA1 (d) reducing the reaction mixture and thus obtained polyalkene to a finely divided state at a cryogenic temperature below the glass transition temperature of the drag reducing polyalkene.
The surfactant is employed to reduce the viscosity of the slurry but it does not improve drag reduction as is evident from the statement "the use of a surface active agent results in systems which are characterized by improved handling characteristics such as fluidity, pumpability, and/or pourability. Though the viscosity of the system is significantly decreased, the hydrodynamic drag reduction efficiency characteristics remain particularly unaffected" (Col. 1, lines 21-27). Data to support this statement is shown in Table 2 of the patent.
It is emphasized that in that patent, the carrier fluid is miscible with water and the drag reduction occurs in water. This is contrasted to the invention at hand in which the carrier fluid of the slurry is not miscible with the hydrocarbon in which drag reduction occurs. In the invention at hand, the surfactant seems to control the onset of dissolution, and thus improve drag reduction efficiency, though the inventors do not wish to be bound to this theory.
Canadian Patent 901,727 deals with a process of continuous polymerization. The process uses two rolls of sheeting which are formed into an envelope with a non-sealed but rolled edge. A liquid polymerization mixture is placed into the cavity formed by joining the two sheets. The process is useful for formation of compounds with polymerizable oxygen functions such as ethers, acetals, ketals, and esters. The enclosure is maintained until the polymerization is complete, whereupon the plastic sheet is recovered and the long strip of polymerized polymer is also recovered.
U.S. Pat. No. 5,244,937 discloses that cryoground drag reducing polymers can be suspended in water using a thickening agent and placed into flowing hydrocarbons as a suspension.
It is an object of the invention at hand to overcome disadvantages of the prior art and to provide a stable non-agglomerating suspension suitable for improving flow of a flowing stream comprised of hydrocarbons upon introduction therein to. Other objects will become apparent to those skilled in the art in view of the disclosure of this application.